1. Field
The present disclosure relates generally to aircraft and, in particular, to a method and apparatus for managing the operation of an aircraft. Still more particularly, the present disclosure relates to a method and apparatus for managing thrust for an aircraft operating at a roll angle.
2. Background
During operation, an aircraft may fly in the air as a result of an aerodynamic force called lift. Lift is generated by the wings of an aircraft as air flows past the wings as a result of forward movement of the aircraft. The wings of an aircraft generate lift because of a pressure reduction on the upper side of the wings. The lower pressure on the upper side of a wing combined with a higher pressure on the underside of the wing provides the lift. Lift may be increased by increasing the angle of the wing cord relative to the airflow. This angle is also referred to as the angle of attack.
When an aircraft performs a turn, the roll angle increases, which increases the angle of attack for the aircraft. With the increase in the angle of attack, drag also may be increased. Without sufficient thrust, the aircraft may slow, further decreasing the wing lift. Further, the aircraft also may change altitude. These changes in the movement of the aircraft are often undesirable during a turn. Instead, it is desirable to maintain the speed of the aircraft into a turn as well as substantially maintaining the altitude of the aircraft.
Existing automatic throttle systems may generate thrust based on a roll angle compensation that is calculated using a versine of the roll angle. A versine is also referred to as a versed sign and is a trigonometric function such as, for example, versine (β)=1−cosine (β). This type of compensation for generating thrust is adequate for aircraft maneuvering at low roll angles, because the versine is an approximation for the reciprocal of cosine of roll. A low roll angle may be around 30 degrees or less. These types of throttle systems for generating thrust are typically inaccurate for roll maneuvers that are above around 25 to around 30 degrees.
Therefore, it would be advantageous to have a method and apparatus that overcomes at least some of the issues described above.